Solid propellant composition containing polyesters and an inorganic oxide burning rate catalyst

ABSTRACT

2. A solid propellant composition comprising a cured intimate mixture of a solid inorganic oxidizing salt, said inorganic oxidizing salt being present in an amount of from about 45 percent to about 90 percent by weight of the total propellant composition; an unsaturated polyester resin consisting of the condensation product of a saturated polyhydric alcohol and polycarboxylic acid, said polyester resin being the condensation product of an alkylene glycol, maleic anhydride and sebacic acid heteropolymerized with an unsaturated compound selected from the group consisting of lower alkenes, lower alkynes, phenyl substituted lower alkenes, lower alkyl dienes, lower alkenyl esters of lower alkanoic acids, lower alkyl esters of lower alkanoic acids, lower alkenyl esters of lower alkanoic acids, allyl diglycol carbonate, diallyl diglycollate, and mixtures thereof; and a burning rate catalyst comprising an inorganic oxide selected from the group consisting of the oxides of vanadium, cobalt, iron, chromium, manganese, copper, silver, and mixtures thereof.

United States Patent [72] Inventor Ralph W. Lawrence Glendora, Calif.

[21 Appl. No. 388,944

[22] Filed Aug. 11, I964 [45] Patented Dec. 21, 1971 17 3 AssigneeAerojet-General Corporation Azusa, Calif.

[54] SOLID PROPELLANT COMPOSITION CONTAINING POLYESTERS AND AN INORGANICOXIDE BURNING RATE CATALYST 3,031,289 4/1962 Philipson 3,058,858 10/1962Batchelderetal ABSTRACT: 2. A solid propellant composition comprising acured intimate mixture of a solid inorganic oxidizing salt, saidinorganic oxidizing salt being present in an amount of from about 45percent to about 90 percent by weight of the total propellantcomposition; an unsaturated polyester resin consisting of thecondensation product of a saturated polyhydric alcohol andpolycarboxylic acid, said polyester resin being the condensation productof an alkylene glycol, maleic anhydride and sebacic acidheteropolymerized with an unsaturated compound selected from the groupconsisting of lower alkenes, lower alkynes, phenyl substituted loweralkenes, lower alkyl dienes, lower alkenyl esters of lower alkanoicacids, lower alkyl esters of lower alkanoic acids, lower alkenyl estersof lower alkanoic acids, allyl diglycol carbonate, diallyl diglycollate,and mixtures thereof; and a burning rate catalyst comprising aninorganic oxide selected from the group consisting of the oxides ofvanadium, cobalt, iron, chromium, manganese, copper, silver, andmixtures thereof.

SOLID PROPELLANT COMPOSITION CONTAINING POLYESTERS AND AN INORGANICOXIDE BURNING RATE CATALYST This invention relates to jet propulsion andprovides improved solid propellant charges capable of good performanceafter or during exposure over a wide range of weather and temperatureconditions.

In the operation of certain types of rocket motors, it is customary toburn a solid charge in a motor chamber to produce a large volume of gasunder pressure, which escapes at high velocity as a gas jet through theexhaust nozzle leading from the chamber producing a resultant highthrust. Typical solid charges have heretofore commonly comprised athermoplastic fuel such as asphalt having mixed with it a finely dividedoxidizing substance in sufficient quantity to burn the fuel. Thismixture is ordinarily formed into a solid mass within the chamber,presenting a surface at which the burning occurs.

Rocket motors are commonly exposed to a large variety of weatherconditions and a wide range of temperature, between the time of theirmanufacture and the time of use. Solid propellant charges of the typeabove described often tend to sag under tropical conditions or becomebrittle and develop cracks at very low temperatures, thus producinglarge and irregular burning surfaces. The formation of enlarged exposedsurfaces or cracks is undesirable as it increases the area for burning,thus accelerating combustion with an attendant pressure rise in themotor chamber which may produce an explosion. There are known solidpropellant charges which do not become unduly brittle or crack in lowtemperatures and are resistant to sagging in tropical environments.These propellants of the so-called solid type are substantiallyhomogeneous in composition and relatively free from cavities and airbubbles. In addition, they may be composited at room temperature,relieving the necessity of heating any of the ingredients at the timethat the oxidizer is incorporated into the resin. These propellantcompositions may be cured at temperatures which do not materially exceed200 F., providing no additional hazard during curing operations.

However, these propellants suffer in having a burning rate which isoften too low for effective operation.

It is an object of this invention to provide burning rate additives forsolid propellants, so that the burning rate of said solid propellants isincreased.

The novel solid propellant charge of this invention comprises anintimate mixture of a finely divided oxidizer together with a burningrate catalyst uniformly distributed in a resinous binder which acts as afuel. The resin comprises a polyester component; that is, the reactionproduct of a polycarboxylic acid with a polyhydric alcohol with whichthere is incorporated a polymerizable unsaturated component such as avinyl, allyl or olefinic compound compatible with the liquid resin.

The polyester component, sometimes known as an alkyd component or alkydresin, must possess some degree of unsaturation in the molecule in orderto permit it to heteropolymerize with the unsaturated component, whichmay be, for example, phenyl substituted lower alkenes such as styrene,lower alkenyl esters of lower alkanoic acids such as vinyl acetate,lower alkyl esters of lower alkenoic acids such as esters of acrylic ormethacrylic acid; allyl compounds such as allyl diglycol carbonate,lower alkenyl esters of lower alkenoic acids such as diallyl maleate;diallyl diglycollate; other compounds including lower alkyl dienes suchas butadiene, lower alkynes such as acetylene, etc.; and derivatives ofany of the above substances which will polymerize -with the resin. ingeneral, any unsaturated compound compatible with the resin and whichwill polymerize with it is suitable. This includes essentially allunsubstituted olefins, and in addition, many substituted olefins. Thereason for having unsaturation present in the polyester is to permit theresulting unsaturated polyester to copolymerize with the double bond inthe vinyl or allyl compounds or other unsaturated additives. When asufiicient amount of cross-linkage occurs, the resin becomesthermosetting. With a lesser degree of cross-linkage the resin may bethermoplastic; and in some cases the resin may possess some of theproperties of both thermoplastic and thermosetting resins. All thesetypes of resins are within the scope of the present invention.

The polyester components can be made in general as follows: The hydroxygroups of dihydric or polyhydric alcohols are permitted to react in thepresence of the monomeric vinyl, allyl or other unsaturated componentwith the polycarboxylic groups of, for example, a dicarboxylic acid or amixture of dicarboxylic acids, thereby producing a saturated polyester.The unsaturation to permit the polyester to heteropolymerize with themonomeric vinyl, allyl or other unsaturated component may be supplied byemploying either an unsaturated polyhydric alcohol or an unsaturateddicarboxylic acid. The usual and preferred manner is to employ mixturesof an unsaturated polycarboxylic acid or anhydride with a saturated oraromatic polycarboxylic acid, or anhydride and treating this mixturewith a polyhydric alcohol. The percentage of the unsaturated acid oranhydride should be sufficient to permit the necessary amount ofcopolymerization between the vinyl, allyl or other unsaturated additivein the polyester. The polyester may be present in amounts varyingbetween about 10 percent and about percent by weight, based on theweight of the polyester-unsaturated additive mixture, however, ingeneral, about 50 percent by weight of polyester to about 50 percent byweight of the unsaturated additive produces a satisfactory polyesterresin type of matrix for the propellant.

The alcohols which can be used, are not limited, however, to thedihydric alcohols, as other polyhydric alcohols such as the trihydricand higher polyhydric alcohols may be used. These afford additionalpossibilities for cross-linking and, as a consequence, the toughness andbrittleness of the final resin may be controlled as desired.

For the polyhydric alcohol component, any of the following alcohols maybe used: dihydric alcohols, such as ethylene glycol, diethylene glycol,triethylene glycol, propylene glycol; a trihydric alcohol such asglycerol; tetrahydric alcohols such as the erythritols andpentaerythritol; pentitols which include arabitol, adonitol, xylitol;hexitols including mannitol, sorbitol, dulcitol; and heptitols, forexample persitol and volamitol. Mixtures of any of the above alcoholsmay also be employed, if desired.

Saturated polycarboxylic acids useful in compounding the polyesterresins are, for example the aliphatic dibasic acids, including: oxalic,malonic, succinic, glutaric, adipic, pimelic, sebacic, and azelaic, andthe saturated anhydrides such as succinic anhydride. Examples of theunsaturated carboxylic acids useful as the acidic components in formingpolyester resins are: maleic acid, fumaric acid, citraconic acid,mesaconic acid, and itaconic acid. Examples of aromatic dibasic acids,which are useful in compounding polyester resins, are: phthallic acidand its isomers and naphthalic acid. The anhydrides, such as maleicanhydride, citraconic anhydride, itaconic anhydride and phthallicanhydride, may likewise be used for supplying the desired unsaturation.

Regardless of which of the saturated acids are used, the degree ofunsaturation necessary to provide cross-linkage with the vinyl or allylcompounds or other unsaturated component may be had by the addition ofany of the above-named unsaturated acids or their anhydrides.

In some cases it may be possible to dispense with the use of theforegoing unsaturated polycarboxylic substances; and instead to fonn apolyester resin by modifying the polyester by incorporating into it, amodifying oil which has some degree of unsaturation and is compatiblewith the polyester. From a trace to 1 mole of the modifying oil may beadded to 1 mole of the polyester. Examples of such oils are: castor oil,mustard seed oil, rape oil, haddock liver oil, linseed oil, hemp oil,poppy seed oil, Chinese and Japanese wood oil, tung oil, and olive oil.The unmodified or modified resin may then be blended with the allyl,vinyl compounds or other monomer described above, to produce mixtureswhich are capable of being polymerized into the cross-linked type ofthermosetting resin or the modified resin may be employed withoutfurther additives.

This solid propellant comprises a uniform dispersion of the finelydivided inorganic oxidizer and a polyester resin matrix of the typedescribed above. The resin acts as a binder, and regardless ofsubstituents in the molecule will serve as a fuel if the propellantcontains a sufficient amount of the oxidizer to insure the necessaryoxidation of the organic material; usually all of the carbon is oxidizedto CO and one-third of the hydrogen is oxidized to water. As statedabove, the preferred condensation product is obtained by reacting thepolyhydric alcohol with the polycarboxylic acid having a predetermineddegree of unsaturation in the molecule. An especially useful form ofthis condensation product is the reaction product of sebacic acid and apolyhydric alcohol such as propylene glycol, to which there has beenadded a small amount of unsaturated anhydride such as maleic anhydride.This product is commonly called a modified alkyd resin.

The percentage of unsaturation in the polyhydric alcohol polycarboxylicacid mixture to form the polyester should be between about 2 and 100percent by weight, based on the weight of the total polycarboxylic acidor polycarboxylic acid mixture. The preferred percentage of unsaturationis between about and about percent by weight, based on the weight of theacidic component. Although the polyhydric alcohol and polycarboxylicacid will react in stoichoimetric proportions, nevertheless it is abetter practice to use an excess of the polyhydric alcohol beyond thestoichoimetric amount; and then remove the excess alcohol from thefinished polyester, in order to make the resulting product substantiallyfree from unnecessary matter or impurities.

For the oxidizer, it is preferable to use any stable, solid, inorganicoxidizer The oxidizer is a substance which may be incorporated in thepolyester resin unsaturated polycarboxylic unsaturated monomer mixtureby stirring and mixing, and preferably the oxidizer is added to themixture while the resin is in its liquid state. Examples of suitableoxidizers are the inorganic substances including the chromates,dichromates, permanganates, nitrates, chlorates, and perchlorates, suchas the alkali metal salts of these radicals including sodium, potassium,lithium, rubidium and cesium; and also the nonmetallic salts, forinstance, ammonium or hydrazine of the same radicals. The selection ofthe oxidizing material depends upon the type of propellant and thespecific burning properties desired. The preferred oxidizers are theperchlorates, especially the perchlorates of potassium and ammonium. Theamount of oxidizer added to the resinous mixture lies between about 45and about 90 percent by weight of the total propellant composition andthe weight of the unsaturated polyester resin, monomer mixture liesbetween about 55 and about 10 percent of the same propellantcomposition.

Catalytic substances are particularly useful for speeding up the rate ofpolymerization of the polyester resin monomer mixtures with the oxidizeradded. Such catalytic substances are the organic peroxides and theorganic peresters. The temperature used for curing is dependent somewhatupon the nature of the catalyst and the time during which it is desiredto accomplish complete polymerization. Some catalysts such as l-hydroxycyclohexylhydro peroxide or cumene hydroperoxide, are capable ofpolymerizing certain resins at room temperature if the charge ispermitted to cure for a sufficiently long period of time.

The organic peroxides or peresters should be preferably soluble orcompatible with the polyester resin. However, in some instances, even aninsoluble organic peroxide or perester functions as a catalyst as longas it can be made to decompose and liberate a free oxygen radical.Specific example of compounds which are suitable catalysts for thispolymerization reaction are: tertiarybutyl hydroperoxide, cumenehydroperoxide, benzol peroxide, lauryl peroxide, acetobenzoyl peroxide,ditertiary butyl peroxide, methyl ethyl ketone peroxide, l-hydroxycyclohexyl hydroperoxide, and other hydroperoxides which are not toovolatile at the curing temperature. Specific examples of suitableperesters are: tertiary butyl perbenzoate, and ditertiary butyldiperphthalate.

Such catalysts should be present in the unsaturated polyester resinunsaturated monomer mixture during the time it is subjected to thecuring process. In general the weight of the catalyst employed to bringabout this result is approximately 0.5 percent by weight based on theweight of the combined unsaturated polyester resin unsaturated mixture.If desired, larger amounts of the catalyst may be employed than thoseindicated.

In order to increase the burning rate of the solid propellants discussedabove a burning rate catalyst is added to the propellant composition atthe time the oxidizer is added. Catalysts which may be employed toincrease the burning rate of the solid propellant include the oxides ofvanadium, cobalt iron, chromium, manganese, copper, silver and mixturesthereof. Compounds containing more than one of these oxides may also beused. The oxide need not be used directly, but organic compounds whichwill decompose to form the oxide in situ, such as chromicacetylacetonate may also be employed. The weight of catalyst employedbased upon the weight of the total propellant composition is about 0.02percent to about 1.0 by weight. Amounts greater than about 1.0 percentmay be employed but little improvement is obtained when greater amountsof catalyst are used.

The following examples in which parts and percentages are by weightunless otherwise indicated, are not intended to limit the scope of theinvention.

EXAMPLE 1.

A propellant having the following composition was formulated:

NH,ClO, 75.00% Resin A I235; Styrene l LBSZ Cumene hydroperoxide 0.25%Lecithin 10% solution In styrene) 0.50% Cobalt octoate 1% Co" instyrene) 0.05%

Resin A is prepared y reacting moles adipic acid, 20 moles maleicanhydride and L05 moles diethylene glycol.

The propellant formulation was divided into five batches, and to four ofthe batches was added a catalyst composed of copper oxide and chromiumoxide. The analysis was 17 weight percent CuO, 83% Cr O Varied amountsof the catalyst were added in four batches and the propellant was curedfor two days at 70 F. and an additional three days at 185 F. The burningrates of the propellant with a propellant temperature it can be seenfrom the above results that only a few tenths of a percent of theindicated catalyst produces a great increase in the burning rate of thepropellant.

EXAMPLE 2.

A propellant was prepared and cured for 1 day at ll0 F. and then for 2days at F., using two different varieties of a copper chromite catalyst;a mixture of manganese oxide,

copper oxide, silver oxide and cobalt oxide; and chromicacetylacetonate. The compositions and burning rates are as follows:

Batch 1 2 3 4 NH4ClO4.. 76.00 76.00 76.00 75. 36

Resin B 14.11 14.11 14.11 13.99

Styrene... Cumene hydroperoxide t-Butyl catechol (10% in sty Dioctylsodium sulfosuccinate (10% styrene) 17% 01103837 CF10; 42% C1101 58%c1103-- 50% M1102, 30% CuO, 0010s, 6%

AgzO Chromic acetylacetonate (21.8% CuO,) Burning rates in secf at 1,000p.s.i.a.,

l Resin B is prepared by reacting 80 moles adipic acid, moles maleicanhydride and 1.20 moles diethylene glycol.

mate mixture of a solid inorganic oxidizing salt, a cross-linkedpolymerized polyester resin styrene mixture, the polyester resin beingthe condensation product of propylene glycol, maleic anhydride andsebacic acid, said inorganic oxidizing salt being present in an amountbetween about 45 and about percent by weight of the total propellantcomposition, and a burning rate catalyst comprising an inorganic oxideselected from the group consisting of the oxides of vanadium, cobalt,iron, chromium, manganese, copper, silver, and mixtures thereof.

2. A solid propellant composition comprising a cured intimate mixture ofa solid inorganic oxidizing salt, said inorganic oxidizing salt beingpresent in an amount of from about 45 to about 90 percent by weight ofthe total propellant composition; an unsaturated polyester resinconsisting of the condensation product of a saturated polyhydric alcoholand polycarboxylic acid, said polyester resin being the condensationproduct of an alkylene glycol, maleic anhydride and sebacic acidheteropolymerized with an unsaturated compound selected from the groupconsisting of lower alkenes, lower alkynes, phenyl substituted loweralkenes, lower alkyl dienes, lower alkenyl esters of lower alkanoicacids, lower alkyl esters of lower alkanoic acids, lower alkenyl estersof lower alkanoic acids, allyl diglycol carbonate, diallyl diglycollate,and mixtures thereof; and a burning rate catalyst comprising aninorganic oxide selected from the group consisting of the oxides ofvanadium, cobalt, iron, chromium, manganese, copper, silver, andmixtures thereof.

2. A SOLID PROPELLANT COMPOSITION COMPRISING A CURED INTIMATE MIXTURE OFA SOLID INORGANIC OXIDIZING SALT, SAID INORGANIC OXIDIZING SALT BEINGPRESENT IN AN AMOUNT OF FROM ABOUT 45 PERCENT TO ABOUT 90 PERCENT BYWEIGHT OF THE TOTAL PROPELLANT COMPOSITION; AN UNSATURATED POLYESTERRESIN CONSISTING OF THE CONDENSATION PRODUCT OF A SATURATED POLYHYDRICALCOHOL AND POLYCARBOXYLIC ACID, SAID POLYESTER RESIN BEING THECONDENSATION PRODCUT OF AN ALKYLENE GLYCOL, MALEIC ANHYDRIDE AND SEBACICACID HETEROPOLYMERIZED WITH AN UNSATURATED COMPOUND SELECTED FROM THEGROUP CONSISTING OF LOWER ALKENES, LOWER ALKYNES, PHENYL SUBSTITUTEDLOWER ALKENES, LOWER ALKYL DIENES, LOWER ALKENYL ESTERS OF LOWERALKANOIC AICDS, LOWER ALKYL ESTERS OF LOWER ALKANOIC ACIDS, LOWERALKENYL ESTERS OF LOWER ALKANOIC ACIDS, ALLYL DIGLYCOL CARBONATE,DIALLYL DIGLYCOLLATE, AND MIXTURES THEREOF; AND A BURING RATE CATALYSTCOMPRISING AN INORGANIC OXIDE SELECTED FROM THE GROUP CONSISTING OF THEOXIDES OF VANADIUM, COBALT, IRION, CHROMIUM, MANAGANESE, COPPER, SILVER,AND MIXTURES THEREOF.
 2. A solid propellant composition comprising acured intimate mixture of a solid inorganic oxidizing salt, saidinorganic oxidizing salt being present in an amount of from about 45 toabout 90 percent by weight of the total propellant composition; anunsaturated polyester resin consisting of the condensation product of asaturated polyhydric alcohol and polycarboxylic acid, said polyesterresin being the condensation product of an alkylene glycol, maleicanhydride and sebacic acid heteropolymerized with an unsaturatedcompound selected from the group consisting of loweR alkenes, loweralkynes, phenyl substituted lower alkenes, lower alkyl dienes, loweralkenyl esters of lower alkanoic acids, lower alkyl esters of loweralkanoic acids, lower alkenyl esters of lower alkanoic acids, allyldiglycol carbonate, diallyl diglycollate, and mixtures thereof; and aburning rate catalyst comprising an inorganic oxide selected from thegroup consisting of the oxides of vanadium, cobalt, iron, chromium,manganese, copper, silver, and mixtures thereof.